1. Field of the Invention
The present invention relates to a method of manufacturing silicon carbide, and more specifically, to a method of manufacturing silicon carbide powder having a large surface area and small amounts of impurities by synthesis from inexpensive raw materials at low temperatures using a simple manufacturing apparatus.
2. Related Background Art
Silicon carbide is heat and acid resistant, strong, and hard. It can be used as thermal and mechanical functional structure materials for various crucibles, ceramic baking components, abrasion resistant sliding members, heat exchanger tubes, paper components, catalyst carriers, filters, waste incinerator lining materials, heating elements, abrasives, and the like. Further, a silicon carbide single crystal wafer is used in the fields of automobiles and power semiconductors because of its advantage of small power loss in addition to the above-described thermally, chemically, and mechanically stable properties), and a silicon carbide powder material is required as a raw material therefor.
Examples of a method of manufacturing a silicon carbide powder material include: a method involving mixing metal silicon powder and carbon powder and heating the mixture at 1,000 to 1,400° C., as described in “Method of Manufacturing Silicon Carbide Ceramics”, edited by Shigeyuki Somiya and Kichizo Inomata, published by Uchida Rokakuho Pub., 1988 (direct reaction method); a method involving utilizing a reduction reaction by allowing coke to act on silicon dioxide powder at 1,500 to 1,900° C. (reduction carbonization method); a method involving thermally decomposing a compound, such as polycarbosilane, in a nonoxidative atmosphere at 1,300 to 2,000° C. (thermal decomposition method); and a chemical vapor deposition method involving reacting halogenated silicon, such as silicon tetrachloride, with methane at 800 to 2,000° C. (CVD method).
In the direct reaction method, silicon carbide powder to be obtained has a large particle size, and metal silicon tends to remain unreacted. Thus, the direct reaction method requires a long reaction time. Further, in the reduction carbonization method, a reaction temperature is high at 1,500° C. or higher. The reduction carbonization method requires a long reaction time for reacting sufficiently the raw materials of silicon dioxide and carbon. The reduction carbonization method stops if toxic carbon monoxide formed as a by-product is not removed, and thus has a problem in that a removal device and a detoxification device must be installed. The thermal decomposition method requires a reaction temperature of 1,300° C. or higher and is problematic from the viewpoint of a high process cost and the cost of the organic silicon compound for use as a raw material.
The CVD method employs halogenated silicon and methane as raw materials. Thus, the CVD method has problems of not only high raw Material cost, but also formation of toxic hydrogen halides as a by-product through decomposition of the raw materials to thereby damage an apparatus by corrosion. Further, the CVD method requires a reaction temperature of 800° C. at a minimum. A phenomenon of sublimation of an Si element component occurs more readily at higher temperatures in the temperature ranges used for the respective above-mentioned methods. Further, a high reaction temperature leads to a degrading yield problem and is a major factor in increasing the manufacturing cost.
Further, Japanese Patent Application Laid-Open No. H05-279007 discloses a method involving impregnating a cellulose material with water glass, neutralizing sodium silicate with an acidic substance, allowing the cellulose material to carry silica washed with water, baking in an inert atmosphere at 1,000 to 2,000° C., and pulverizing the baked product.
Regarding a method of manufacturing high purity β-silicon carbide powder that can be used for a silicon carbide single wafer, Japanese Patent Application Laid-Open No. H07-157307 discloses a method involving mixing an ethyl silicate monomer and a catalyst for accelerating curing of a resin, such as a phenol resin, carbonizing the mixture in a nitrogen atmosphere at 900° C., and baking the carbonized product in an argon atmosphere at 1,900° C.
However, a high temperature manufacturing apparatus used for each of the above-mentioned methods requiring a high reaction temperature of higher than 800° C. has problems of a longer time for heating and cooling at a higher reaction temperature and a higher running cost at longer reaction times.
Further, at such a high reaction temperature, a particle size of silicon carbide powder to be produced increases to thereby degrade the sintering properties. Thus, a pulverizing step is required for using the silicon carbide powder as a raw material for a sintered molded product. However, the silicon carbide powder is a hard material and has a problem in that impurity elements, such as metals, are mixed in the pulverizing step.
Thus, there is desired a technique of manufacturing a silicon carbide material having a small particle size applicable to various uses and small amounts of impurities at low cost. A small particle size can be adjusted through simple thermal treatment, and thus, a method of reducing a silicon carbide synthesis temperature is required.